Cellulose is a linear polysaccharide of glucose residues connected by .beta.-1,4 linkages. In nature, cellulose is usually associated with lignin, other polysaccharides such as pectin, and hemicelluloses such as xylan. These components must be extracted from the cellulose in many instances to form an acceptable commercial pulp or paper product.
In the pulp and paper industry, cellulose pulp obtained by sulphate cooking in particular is brown, mainly because of lignin remaining in the pulp. Lignin is currently removed by bleaching, whereby the pulp is rendered usable for high-quality paper and cardboard products. Unbleached pulp contains 3 to 5 percent residual lignin. This residual lignin may be linked to hemicelluloses with covalent bonds. Residual lignin is traditionally removed in a multi-stage bleaching procedure using a combination of chlorination (the bleaching) and extraction stages.
The effluent from such bleaching plants is a growing environmental concern due to its content of numerous chlorinated substances, including chlorinated phenols and dioxines. Chlorine is further bound to residues of lignin and acids which are still left in the cellulose pulp after completed bleaching. This residual chlorine ends up in the environment, when paper and cardboard products are discarded. There is therefore a great interest in reducing the use of chlorine compounds like pure chlorine gas, chlorine dioxide or sodium or potassium hypochlorite.
The use of purified hemicellulose hydrolyzing enzymes for some processes in pulp and paper processing is known (WO 89/08738, EP 341,947, EP 334,739 and EP 262,040). For biobleaching purposes, the addition of purified hemicellulose hydrolyzing enzymes, by degrading lignin-hemicellulose complexes, may avoid or diminish the use of chlorine compounds in the bleaching processes of cellulose pulp (Kantelinen, Kemia Kemi 15(3):228-231 (1988)). Alternatively, or at the same time, pectin and/or lignin may be decomposed with pectin and/or lignin degrading enzymes, respectively. However, the isolation of purified enzymes at levels naturally produced from native sources for use in these processes is timeconsuming, tedious and very expensive on a large scale.
Costs can be lowered by using a conventional (cell homogenate or lysate preparation) crude enzyme preparation which contains a desired enzyme. However, crude preparations of these enzymes are usually obtained from fungal sources and further contain undesired enzymes, for example, cellulases, whose addition is detrimental to the production of the pulp or paper end product.
Consequently, there is a clear demand for enzyme preparations, which contain unique enzyme profiles, tailormade, that is, designed specifically for the purposes of the industry in which they are to be used, and which can be obtained in a cost-effective manner, such as, for example, directly from the culture medium of a microorganism which has been modified so that it produces the desired enzymes, but not appreciable quantities of undesired enzymes.